Reinnervation of original synaptic sites on muscle fiber basement membrane after disruption of the muscle cells.

Regenerating axons form new synapses precisely at sites of original synapses in denervated skeletal muscle. To determine what role the muscle cell plays in this phenomenon, we studied reinnervation of frog muscle at intervals after crushing the nerve and damaging the muscle fibers. Damaged muscle fibers degenerate and are phagocytized, but their basement membrane persists and acts as a scaffold for regenerating muscle cells. Specializations of the basement membrane serve to mark original synaptic sites after nerve and muscle have degenerated. Regenerating axons enter the region of damage and form functional synapses with regenerating myofibers. The new nerve terminals are found almost exclusively at the original synaptic sites, demonstrating that the integrity of the original postsynaptic cell is not necessary for topographically precise reinnervation of denervated muscle.